In German Patent No. 698 05 955 T2, a method is described for the drowsiness monitoring of a vehicle driver, in which the circadian rhythm, which characterizes the biological functioning of the driver in daytime rhythm, is ascertained, and a warning is output in case a certain state of drowsiness is detected. Since the biological functioning of persons is subject to a time-of-day rhythm, the current state of drowsiness according to German Patent No. 698 05 955 T2 is ascertained as a function of the clock time. In addition, individual deviations of the circadian curve from reference values are taken into account, which are ascertained by the use of sensors from the driving behavior, for instance, the steering operation of the driver.
In U.S. Published Patent Application No. 2010/0079294 A1, an attention detection system is described, in which the various biological rhythms of human beings is observed, in order to ascertain the current state of attentiveness. In this case, the circadian rhythm is also taken into account, which represents day and night influences, as well as the homeostatic rhythm for the effect of preceding sleeping and waking phases. In order to determine at which current point of the circadian rhythm one is located, sensor data of a light sensor are evaluated.
A method for detecting the reaction preparedness of a driver of a motor vehicle is known from German Published Patent Application No. 103 59 125 A1 which is based on the evaluation of the pupil reflexes. During driving, the pupil of the driver is monitored using a camera, and a conclusion is drawn on the degree of drowsiness of the driver from the pupil reflex.